Huge thanks to the Ultimate Commodore 64 Reference, which I used to auto-generate a lot of code.
go run ./Emulator will start in debug mode:
------------+
instruction | LDX #$FF (load)
registers | PC: FCE2 S: FF A: 00 X: 00 Y: 00
status | N: 0 V: 0 -: 0 B: 0 D: 0 I: 1 Z: 0 C: 0
memory | FCE2: A2 FF 78 9A D8 20 02 FD
interrupts | Pending: false Vector: FFFC
------------+
debug>
Use the help command to list commands.